1. Field of the Invention
The present invention relates to a laser oscillator using a semiconductor laser, and a light scattering type particle detector for detecting particles contained in sample fluid using the laser oscillator.
2. Description of the Prior Art
In a conventional light scattering type particle detector as shown in FIG. 22, a laser oscillator comprises a laser medium 200 and a reflecting mirror 201, and a flow path 202 defined by fluid to be detected is provided between the laser medium 200 and the reflecting mirror 201. Pumping laser light Le emitted from a semiconductor laser 203 is condensed with a condenser lens 204 to irradiate upon the laser medium 200, and thereby the laser medium 200 is pumped. A particle detecting region 205 is a region where laser light La resonating between the laser medium 200 and the reflecting mirror 201 intersects the flow path 202. Scattered light Ls being a scattered portion of the resonating laser light La in the particle detecting region 205 is received at a light receiving portion 206. Particles contained in sample fluid are detected by electrical signals generated based on the intensity of the scattered light Ls which is received.
Further, in the prior art as disclosed in Japanese Patent Publication No. 6-58318, an antireflection coating through which the pumping wavelength of the semiconductor laser 203 (the pumping wavelength of the laser medium 200) can penetrate and a high reflection coating having a characteristic of reflecting the oscillating wavelength of the laser medium 200 are applied onto the surface of the laser medium 200 opposite to the condenser lens 204.
The conventional light scattering type particle detector as shown in FIG. 22 has a drawback that the pumping laser light Le is incident on the semiconductor laser 203 as feedback light even with the antireflection coating through which the pumping wavelength of the semiconductor laser 203 can penetrate. Another drawback exists wherein the laser light La resonating between the laser medium 200 and the reflecting mirror 201 penetrates through the laser medium 200 so as to be incident on the semiconductor laser 203 as feedback light even with the high reflection coating having a characteristic of reflecting the oscillating wavelength of the laser medium 200. Such feedback light causes fluctuation to the intensity of the pumping laser light Le emitted from a semiconductor laser 203 and the resonating laser light La and such fluctuation deteriorates the signal/noise ratio. It is acknowledged that when laser light emitted from the semiconductor laser is later incident on the semiconductor laser again because of reflection or the like, such feedback light causes fluctuation noise.
In another conventional light scattering type particle detector as shown in FIG. 23, a laser oscillator comprises a laser medium 215 and a reflecting mirror 216, and a flow path 217 defined by fluid to be detected is provided between the laser medium 215 and the reflecting mirror 216. Pumping laser light Le emitted from a semiconductor laser 218 is condensed with a condenser lens 219 to irradiate upon the laser medium 215, and thereby the laser medium 215 is pumped. A particle detecting region 220 is a region where laser light La resonating between the laser medium 215 and the reflecting mirror 216 intersects the flow path 217. A scattered portion of the resonating laser light La in the particle detecting region 220 is received at a light receiving portion (not shown in the drawing). Particles contained in the sample fluid are detected by electrical signals generated based on the intensity of the scattered light which is received.
A case is comprised of a hollow first setting block 222 and a hollow second setting block 223. The laser medium 215 is fixed to the second setting block 223 and the second setting block 223 is fixed to the first setting block 222. A light receiving case (not shown in the drawing) for housing the light receiving portion is fixed to the side surface of the first setting block 222.
If there is no error in the fixation of the laser medium 215 to the second setting block 223 or the like, laser light La irradiated from the laser medium 215 goes in the perpendicular direction with respect to the end surface (irradiation surface) of the laser medium 215 and in the direction corresponding to the core axis of the first setting block 222.
However, in fact, error arises in the fixation of the laser medium 215 to the second setting block 223, and resultantly the laser light La is not oriented to travel in the direction corresponding to the core axis of the first setting block 222. In this case, it is necessary to adjust the setting angle of the reflecting mirror 216 with respect to the first setting block 222 so that the laser light La reflected by the reflecting mirror 216 can reflect accurately to the laser medium 215.
Further, even if the setting angle of the reflecting mirror 216 is adjusted to be the most preferable angle to make the laser light La reflected by the reflecting mirror 216 reflect accurately to the laser medium 215, the irradiating direction of the oscillated laser light La does not coincide with the core axis of the first setting block 222. Therefore, it may be necessary to shift the flow path 217 which is positioned on the assumption that the irradiating direction of the oscillated laser light La coincides with the core axis of the first setting block 222. The shift of the flow path 217 changes the position of the particle detecting region 220. Depending on this, it is necessary to adjust the setting position of the light receiving case for housing the light receiving portion with respect to the first setting block 222.
Accordingly, the conventional light scattering type particle detector exhibits drawbacks including that complicated adjustment is required for the position adjustment of the flow path 217 and the setting adjustment of the light receiving case with respect to the first setting block 222, and that a lot of work is also required for the assembly of the whole apparatus, including tasks such as setting the angle adjustment of the reflecting mirror 216 in the case where there is error in the fixation.
Further, as other light scattering type particle detectors, two types as disclosed in Japanese Patent Publication No. 6-58318 are known. One type uses a Hexe2x80x94Ne gas laser as a laser medium and the other uses a solid-state laser as a laser medium.
In either type, a flow path 232 defined by sample fluid flowing from an inlet 230 to an outlet 231 is provided within a laser resonator as shown in FIG. 24. A particle detecting region 233 is a region where laser light La having a circular transverse mode pattern intersects the flow path 232.
Recently, there is a tendency that electronic devices of high precision are manufactured in clean surroundings such as a clean room. The number of particles suspending within a clean room is controlled so as to ensure the cleanness of the clean room. It is required that a large volume of sample air is taken into a particle detector for controlling the number of particles in the clean room.
Therefore, it is necessary to increase the cross section of a flow path for flowing a large volume of sample air through the flow path within a predetermined period of time. Also, it is necessary to increase the cross section of laser light in accordance with the cross section of the flow path and thereby define a larger particle detecting region for detecting all particles within sample air passing the flow path.
However, if the cross section of laser light is increased in the conventional light scattering type particle detector, the following problems are caused:
(1) In a light scattering type particle detector using Hexe2x80x94Ne gas laser as a laser medium, a Hexe2x80x94Ne laser medium is comprised of a capillary glass tube having a circular cross section and thereby the transverse mode pattern of laser light is made circular. If such a circular cross section of laser light is broadened, the energy density is decreased and the amount of scattered light is decreased. Therefore, it is difficult to detect fine particles.
(2) In a light scattering type particle detector using a solid-state laser as a laser medium, the surface of the irradiating lens of a pumping light source and the surface of the reflecting mirror are formed to have a spherical shape and thereby the transverse mode pattern of laser light is made circular. If such a circular cross section of laser light is broadened, the energy density is decreased and the amount of scattered light is decreased. Therefore, it is difficult to detect fine particles with accuracy.
(3) In the conventional art, for defining a larger particle detecting region without reducing the energy density, it is necessary to use a laser medium having a longer and thicker glass tube in the case of Hexe2x80x94Ne gas laser. Also, it is necessary to use a pumping light source having a high output in the case of a solid-state laser. In both cases, a large-scale device and high costs are required.
Further, since the cross section of laser light expands circularly, the volume of a particle detecting region is increased and scattered light generated by air molecules in the detecting region is increased. Therefore, the increase of noise is caused by the increase of such background light and it becomes difficult to detect fine particles with accuracy.
For solving the above-mentioned drawbacks, according to an aspect of the present invention, there is provided a laser oscillator in which laser light is irradiated by pumping a laser medium using pumping laser light generated from a semiconductor laser, wherein the pumping laser light generated from the semiconductor laser is condensed to irradiate upon the laser medium with a concave mirror and the core axis (chief ray) of the pumping laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the laser medium.
With this, since the pumping laser light generated from the semiconductor laser is condensed to irradiate upon the laser medium with the concave mirror and the core axis (chief ray) of the pumping laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the laser medium, it is possible to prevent the pumping laser light from irradiating back upon the semiconductor laser, prevent fluctuation in the intensity of the pumping laser light, and thereby reduce any fluctuation in the intensity of the laser light which is irradiated from the laser medium.
According to another aspect of the present invention, a light scattering type particle detector, using a semiconductor laser as a light source, for detecting particles contained in sample fluid which defines a flow path, wherein laser light generated from the semiconductor laser is irradiated upon the flow path with a concave mirror and thereby a particle detecting region is defined.
With this, since laser light generated from the semiconductor laser is condensed with the concave mirror and the laser light is allowed to irradiate the particle detecting region, it is possible to prevent the laser light generated from the semiconductor laser from irradiating back upon the semiconductor laser and thereby to reduce the fluctuation in the intensity of the laser light generated from the semiconductor laser. Therefore, it is possible to accurately detect particles having a relatively small diameter.
According to another aspect of the present invention, a light scattering type particle detector, using a semiconductor laser as a light source, for detecting particles contained in sample fluid which defines a flow path, wherein laser light generated from the semiconductor laser is condensed to irradiate upon the flow path with a concave mirror and a condenser lens, and thereby a particle detecting region is defined, and wherein the core axis (chief ray) of the laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the condenser lens.
With this, since laser light generated from the semiconductor laser is reflected on a concave mirror and condensed with a condenser lens, and thereby the particle detecting region is irradiated, and also the core axis (chief ray) of the laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the condenser lens, it is possible to prevent the laser light generated from the semiconductor laser from irradiating back upon the semiconductor laser and thereby to reduce the fluctuation in the intensity of the laser light generated from the semiconductor laser. Therefore, it is possible to accurately detect particles having a relatively small diameter.
According to another aspect of the present invention, there is provided a light scattering type particle detector in which a laser medium is pumped by pumping laser light generated from a semiconductor laser, laser light irradiated from the laser medium is irradiated to a flow path defined by sample fluid whereby a particle detecting region is defined, particles contained in the particle detecting region are detected, wherein the pumping laser light generated from the semiconductor laser is condensed to irradiate upon the laser medium with a concave mirror and the core axis (chief ray) of the pumping laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the laser medium.
With this, since the pumping laser light generated from the semiconductor laser is condensed to irradiate upon the laser medium with a concave mirror and the core axis (chief ray) of the pumping laser light which is reflected on the concave mirror has a predetermined angle with respect to the optical axis of the laser medium, it is possible to prevent the pumping laser light from irradiating back upon the semiconductor laser, to prevent the fluctuation in the intensity of the pumping laser light, and thereby to reduce the fluctuation in the intensity of the laser light irradiated from the laser medium. Therefore, it is possible to accurately detect particles having a relatively small diameter.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a semiconductor laser is condensed to irradiate upon a laser medium with a condenser lens, the laser medium is pumped, and thereby laser light is irradiated, wherein the optical axis of the semiconductor laser has a predetermined angle with respect to the optical axis of the laser medium.
With this, since the optical axis of the semiconductor laser has a predetermined angle with respect to the optical axis of the laser medium, it is possible to prevent the pumping laser light from irradiating back upon the semiconductor laser, to prevent the fluctuation in the intensity of the pumping laser light, and thereby to reduce the fluctuation in the intensity of the laser light irradiated from the laser medium.
According to another aspect of the present invention, there is provided a light scattering type particle detector in which the laser light irradiated from the above-mentioned laser oscillator is irradiated to a flow path defined by sample fluid, and thereby a particle detecting region is defined, particles contained wherein being detected by receiving scattered light generated by the laser light.
With this, since the optical axis of the semiconductor laser has a predetermined angle with respect to the optical axis of the laser medium, it is possible to prevent the pumping laser light from irradiating back upon the semiconductor laser, to prevent the fluctuation in the intensity of the pumping laser light, and thereby to reduce the fluctuation in the intensity of the laser light irradiated from the laser medium. Therefore, it is possible to accurately detect particles having a relatively small diameter.
According to another aspect of the present invention, there is provided a light scattering type particle detector comprising a laser medium pumped by pumping laser light, a reflecting mirror on which laser light irradiated from the laser medium is reflected, a flow path defined by sample fluid, and being provided between the laser medium and the reflecting mirror, and a particle detecting region defined by irradiating the laser light to the flow path, the light scattering type particle detector being for detecting particles contained in the particle detecting region by receiving scattered light generated by the laser light, wherein the optical axis of the laser medium and the optical axis of the reflecting mirror are allowed to coincide with each other and a setting angle adjusting means is provided for adjusting setting angles of the laser medium and the reflecting mirror with respect to a setting block for each so as to make the optical axes intersect the flow path.
With this, since setting angles of the laser medium and the reflecting mirror can be adjusted, it is not required to adjust the position of the flow path or a light receiving portion and thereby it is possible to easily adjust the fixation.
According to another aspect of the present invention, in the above-mentioned light scattering type particle detector, the setting angle adjusting means comprises a laser medium setting member to which the laser medium is fixed, the setting angle of which laser medium setting member is adjustable with respect to the setting block for the laser medium, a reflecting mirror setting member to which the reflecting mirror is fixed, the setting angle of which reflecting mirror setting member is adjustable with respect to the setting block for the reflecting mirror, elastic members which are interposed between the laser medium setting member and the setting block for the laser medium and between the reflecting mirror setting member and the setting block for the reflecting mirror.
With this, since the laser medium is fixed to the laser medium setting member, the setting angle of which laser medium setting member is adjustable with respect to the setting block for the laser medium, and the reflecting mirror is fixed to the reflecting mirror setting member, and the setting angle of which reflecting mirror setting member is adjustable with respect to the setting block for the reflecting mirror, it is possible to easily adjust the setting angles of the laser medium and the reflecting mirror.
Further, since elastic members are interposed between the laser medium setting member and the setting block for the laser medium and between the reflecting mirror setting member and the setting block for the reflecting mirror respectively, it is possible to smoothly adjust the setting angles of the laser medium and the reflecting mirror because of the tension between the components created by the elasticity of the elastic members.
According to another aspect of the present invention, in the above-mentioned light scattering type particle detector, the elastic members are O-rings comprised of rubber.
With this, since O-rings comprised of rubber are used, the internal space in which the laser medium and the reflecting mirror are provided is sealed from the outside. As a result of this, air or the like outside of the apparatus cannot enter the internal space and the laser medium or the reflecting mirror is not contaminated.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a semiconductor laser is condensed to irradiate upon a laser medium with a condenser lens, the laser medium is pumped, and thereby laser light is irradiated, wherein a setting position adjusting means for the semiconductor laser is provided for superposing the intensity distribution (mode) of the pumping laser light generated from the semiconductor laser on the intensity distribution (mode) of the laser light irradiated from the laser medium.
With this, it is possible to make the optical axis of the semiconductor laser coincide with the optical axis of the laser medium. As a result of this, by effectively utilizing the pumping laser light, it is possible to maximize the output.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a semiconductor laser is condensed to irradiate upon a laser medium with a condenser lens, the laser medium is pumped, and thereby laser light is irradiated, wherein a setting position adjusting means for the condenser lens is provided for superposing the intensity distribution (mode) of the pumping laser light generated from the semiconductor laser on the intensity distribution (mode) of the laser light irradiated from the laser medium.
With this, it is possible to make the condensing position of the pumping laser light coincide with a desired position of the laser medium. As a result of this, by effectively utilizing the pumping laser light, it is possible to maximize the output.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a semiconductor laser is condensed to irradiate upon a laser medium with a condenser lens, the laser medium is pumped, and thereby laser light is irradiated, wherein a setting position adjusting means for the semiconductor laser and a setting position adjusting means for the condenser lens are provided for superposing the intensity distribution (mode) of the pumping laser light generated from the semiconductor laser on the intensity distribution (mode) of the laser light irradiated from the laser medium.
With this, it is possible to make the optical axis of the semiconductor laser coincide with the optical axis of the laser medium and it is also possible to make the condensing position of the pumping laser light coincide with a desired position of the laser medium. As a result of this, by effectively utilizing the pumping laser light, it is possible to maximize the output.
According to another aspect of the present invention, there is provided a light scattering type particle detector in which the laser light irradiated from the above-mentioned laser oscillator is directed to a flow path defined by sample fluid, and thereby a particle detecting region is defined, particles contained in which particle detecting region are detected by receiving scattered light generated by irradiating the laser light onto said particles.
With this, it is possible to obtain laser light having high output so as to detect fine particles with accuracy.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a pumping light source is condensed to irradiate upon a solid-state laser with a condenser means and laser light irradiated from the solid-state laser is allowed to irradiate back upon the solid-state laser by a reflecting means, wherein the condenser means has a surface having different radii of curvature in the parallel direction and the perpendicular direction with respect to the flow path.
With this, the pumping laser light generated from the pumping light source is irradiated to the solid-state laser on the condition that the cross section of the pumping laser light is made an elongated shape, and thereby it is possible to make the cross section of the laser light irradiated from the solid-state laser an elongated shape.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a pumping light source is condensed to irradiate upon a solid-state laser with a condenser means and laser light irradiated from the solid-state laser is allowed to go back to the solid-state laser by a reflecting means, wherein the reflecting means has a surface having different radii of curvature in the parallel direction and the perpendicular direction with respect to the flow path.
With this, the laser light irradiated from the solid-state laser is allowed to go back to the solid-state laser by reflecting from the reflecting means which has a surface having different radii of curvature in the parallel direction and the perpendicular direction with respect to the flow path, and thereby it is possible to make the cross section of the oscillated laser light an elongated shape.
According to another aspect of the present invention, there is provided a laser oscillator in which pumping laser light generated from a pumping light source is condensed to irradiate upon a solid-state laser with a condenser means and laser light irradiated from the solid-state laser is allowed to go back to the solid-state laser by a reflecting means, wherein both of the condenser means and the reflecting means have surfaces having different radii of curvature in the parallel direction and the perpendicular direction with respect to the flow path.
With this, the pumping laser light generated from the pumping light source is irradiated to the solid-state laser on the condition that the cross section of the pumping laser light is made an elongated shape, the laser light irradiated from the solid-state laser is allowed to irradiate back upon the solid-state laser by reflecting from the reflecting means which has a surface having different radii of curvature in the parallel direction and the perpendicular direction with respect to the flow path, and thereby it is possible to make the cross section of the oscillated laser light an elongated shape.
It is also possible thereby to effectively utilize the pumping laser light and increase the intensity of the oscillated laser light.
According to another aspect of the present invention, there is provided a light scattering type particle detector in which the laser light irradiated from the above-mentioned laser oscillator is directed to a flow path defined by sample fluid, and thereby a particle detecting region is defined, particles contained in which particle detecting region are detected by receiving scattered light generated by irradiating the laser light on said particles.
With this, by using laser light having an elongated shape in the transverse mode pattern, it is possible to broaden the particle detecting region without deteriorating the energy density (intensity) of the laser light.